344 
Francis B. Sumner 
jected was continued (though to a qualified extent) during the earlier 
stages of i)regnancy of the mothers. This interpretation is subject 
to the same objections as the preceding. It is obvious that in a 
warm-blooded animal the fetus could not be directly affected by dif- 
ferences of temperature as such. And, even if we grant some indirect 
influence upon the fetus, it would be curious indeed if the parental 
modifications should be so closely paralleled. 
Deserving more serious consideration, we believe, are the fol- 
lowing possible interpretations of these results: 
E. The differences may have been due, not to any specific in- 
fluence (hereditary or otherwise) which has affected the tail, foot or 
ear directly, but to some general constitutional difference in the off- 
spring of the two sets of parents. In other words, these differences 
in the length of the peripheral parts may be correlated with some 
constitutional difference of a very general sort\]. In this connection, 
it must be admitted that the offspring of the warm-room mice showed 
a very much higher mortality (40 per cent between the first and se- 
cond measurements) than those of the cold-room mice (20 per cent). 
The former were likewise somewhat larger, on the average, when 
measured at the age of three months. Thus there did appear to exist 
some sort of a constitutional difference, at least as regards certain 
individuals. We should not be justified, however, in assuming any 
such difference in constitution between surviving mice of equal size, 
and these it was which have been compared in our tables. And in 
any case, we do not thus far have the least evidence that the length 
of these appendages is correlated with any such congenital differ- 
ences in constitution. 
F. An explanation closely similar to the last would be that the 
general stage of development in one lot of mice had been accelera- 
ted or retarded as compared with that of the other. We know that 
the ears and feet of young mice are relatively much larger than those 
of older ones. It might be contended, therefore, that the warm-room 
descendants were in a relatively more juvenile condition, as a result, 
perhaps, of an enfeeblement to which their parents had been sub- 
jected. This supposition is hardly in accord, however, with the fact 
1) Hatai Journal of Comparative Neurology and Psycholog-y. 1908; be- 
lieves that he has demonstrated for white rats that underfeeding produces short 
tailed individuals. Since this conclusion appears to be based upon a consider- 
ation of only five underfed animals, it cannot be regarded as proven. On the 
other hand, there is nothing improbable about it. 
